A phenomenon in which pressure within a pipe suddenly rises or suddenly drops due to a sudden change of the velocity of a moving fluid in a pipeline is called a water impact phenomenon (or water-hammering phenomenon).
If a stopped pump is suddenly driven without a proper manipulation of a valve, power is suddenly off during a normal operation, or power is instantaneously blocked by a cutoff valve at the end of a pipeline, the velocity of a moving fluid within the pipeline suddenly changes and thus pressure within the pipeline greatly rises or drop to generate a severe impact, thereby generating water-hammering pressure. In daily life, when the tap water of a washbowl is suddenly locked by one lever while the tap water is used, an exposed water pipe generates a sound along with vibration due to the water-hammering phenomenon. The water-hammering phenomenon has a possibility that it may cause a great accident in a large-sized road/water transmission pipeline that supplies a large amount of water other than a common home. The influence of damage (the stop of water, road/residential area flooding, etc.) attributable to the accident is very great.
As shown in FIG. 1, from a graph in which a change of pressure/water level is changed over time, a normal/safety/water-hammering state can be easily checked from a change in pressure and the water level generated in the pipeline.
A sudden change in pressure is greatly influenced by a change in the velocity of a moving fluid within the pipe. An acting force depending on the size of a cross section may be calculated. The size of the pipe is large and the apparatus is complicated in a common large water transmission line compared to the pipeline for home use. Accordingly, a safe operation is required by incorporating the influence.
A change in pressure generated due to a sudden change in speed does not act on one place, but is delivered along the pipe through a method, such as propagation or reflection, and has an effect. This may be easily understood through the delivery phenomenon of an echo in the air. The air may be easily diffused, but is less influenced by another medium within the pipe and may have a great influence on the pipe for a long time due to the characteristics of water, that is, a non-compression fluid, through the pipe having stiffness of a specific size.
In general, during the normal operation of the pump, as shown in FIG. 2, pressure is maintained like a hydraulic grade line. In a pressure distribution in the pipeline attributable to a power failure or malfunction, in a specific section, dropping pressure is lowered compared to a hydrostatic head. Rising pressure appearing due to the reflection of a pressure wave after a specific time may rise up to a level that exceeds allowable pressure in which the pipe or device can withstand in a worse case. If pressure in the pipe becomes lower than −5˜−7 mAq, that is, pressure according to equipment criteria regulated by the Environment Bureau, installing water-hammering prevention equipment must be reviewed because column separation may occur.
As described above, a phenomenon in which a pressure wave generated due to a sudden change in speed or pressure of a moving fluid flowing within the pipe is propagated along the pipeline is called a water-hammering action.
The water-hammering action gives damage to a variety of types of facilities, such as a pump, valve and turbine connected to a pipe, in addition to the pipe, causing the waste of a high cost and time, vibration and noise. Accordingly, thorough preparation for such damage is required upon designing the pipeline design. In accordance with the recent examinations through technical diagnosis or site investigation, accurate design factors have not yet been applied to many facilities (the conduct pipe of a water power plant, a variety of types of water supply facilities including high-capacity wide waterworks equipment, and a variety of types of water pipeline facilities), but a water-hammering equipment has been chiefly installed. Accordingly, the budget is wasted due to excessive equipment or the function of water-hammering reduction equipment does not properly operate due to excessively insufficient equipment capacity.
Accordingly, in order to establish proper measures for this problem, a safe operation needs to be performed by installing a variety of types of water-hammering facilities (the installation of a flywheel, the installation of a surge tank, the installation of a stand pipe, the installation of an air chamber, the installation of an air valve, the installation of a safety valve, a change of a pipeline shape, etc.) (hereinafter, an expression “apparatus” is interchangeably used) capable of reducing and controlling the water-hammering action by carefully deriving important design factors in water-hammering analysis from the beginning of the design.
Recently, there is a need for a technology for previously predicting a dangerous factor by incorporating an accurate design factor into computer computation analysis when equipment or water-hammering equipment is designed in order to secure stability. Regarding a method of reducing water-hammering damage, more accurate analysis is made possible through computation analysis. However, the results of the evaluation for water-hammering equipment are quite different depending on which variable is applied to a prevention apparatus and whether characteristics are incorporated into the prevention apparatus in the water-hammering computation analysis.
Common water-hammering equipment has a problem in storing operating information and requires a lot of time using expensive additional equipment in order to analyze the operating information. Furthermore, in order to install the normal water-hammering equipment, separate processing must be performed on the existing facility or apparatus or many types of equipment must be attached to the facility. Data can be obtained only in a specific period because an experiment apparatus must be installed after the operation of the water-hammering equipment is stopped, and a task must be performed according to a separate schedule because a data acquisition apparatus must be removed after the analysis of data is finished.
In order to reduce water-hammering damage, the water-hammering prevention apparatus must be installed in a site, operating data must be obtained, and the water-hammering prevention apparatus must be developed or driven using the results. If limited information obtained in some sites is applied to the entire system, it is difficult to secure performance that guarantees safety. Furthermore, if a situation is different, the apparatus operates based on previous data, frequently leading to a danger of an accident.
A current water-hammering prevention apparatus company adopts only data that belongs to previous experimental data related to many sites and that has been determined to have the best performance, promotes only such a portion, and incorporates it into the entire system in order to protect all facilities through the same performance. In this case, however, an accident is caused, and equipment that must require the water-hammering prevention apparatus does not obtain satisfactory results for performance from a user. As a result, pieces of equipment as a safety apparatus are shunned by the entire industry and industrial companies, and thus a danger of an accident rises day by day.
Furthermore, the water-hammering action needs to be subject to reasonable analysis because it has many difficulties in analysis. Although the water-hammering prevention apparatus is installed based on the reasonable analysis, it is difficult to obtain a desired effect if systematic management is not performed. It is very difficult to analyze the water-hammering action through simple calculation according to a common numerical calculation method based on the existing water and sewage equipment criteria regulated the Environment Bureau. Accordingly, a method according to a computation analysis program using a computer is chiefly used due to complexity and the difficulty of an analyzed equation. Today, most of practical designers calculate all of contents based on such computation analysis, but still have a difficulty in obtaining an accurate solution.
In the water-hammering action in the pipeline, a moving fluid flowing within the pipe generates a sudden change in speed due to a failure of the pump or a sudden stop attributable to a power failure, a sudden opening/shutting of the valve, etc. Accordingly, pressure within the pipeline is greatly changed. The pipeline and the apparatus are influenced by a phenomenon in which a pressure wave generated at this time propagates.
The water-hammering action gives damage to a variety of types of facilities, such as a pump, valve and turbine connected to a pipe, in addition to the pipe, causing the waste of a high cost and time, vibration and noise. Accordingly, thorough preparation for such damage is required upon designing the pipeline design.
However, in accordance with the recent examinations through technical diagnosis or site investigation, accurate design factors have not yet been applied to many facilities (the conduct pipe of a water power plant, a variety of types of water supply facilities including high-capacity wide waterworks equipment, and a variety of types of water pipeline facilities), but a water-hammering equipment has been chiefly installed. Accordingly, the budget is wasted due to excessive equipment or the function of water-hammering reduction equipment does not properly operate due to excessively insufficient equipment capacity.
Accordingly, in order to establish proper measures for this problem, a safe operation needs to be performed by installing a variety of types of water-hammering facilities (the installation of a flywheel, the installation of a surge tank, the installation of a stand pipe, the installation of an air chamber, the installation of an air valve, the installation of a safety valve, a change of a pipeline shape, etc.).